This invention relates to a vehicle hydraulic brake device which permits automatic brake control, particularly to a vehicle hydraulic brake device which can reduce any change in deceleration when shifting from automatic brake control to normal braking without any reduction in safety.
A conventional vehicle hydraulic brake device which makes automatic brake control possible is disclosed in JP patent publication 11-139279.
The vehicle hydraulic brake device includes a hydraulic pressure source for generating a predetermined hydraulic pressure, a pressure adjusting valve for adjusting the output hydraulic pressure of the hydraulic pressure source to a value corresponding to the brake operating force, a master cylinder for producing brake hydraulic pressure by activating a master piston with the output hydraulic pressure of the pressure adjusting valve introduced into a pressure chamber, and the brake operating force, and wheel cylinders activated under the output hydraulic pressure from the master cylinder and imparting braking force to the respective vehicle wheels.
It further includes a solenoid valve for supplying the output hydraulic pressure of the pressure adjusting valve to hydraulic lines extending from the master cylinder to the wheel cylinders, a hydraulic pressure supply passage connected to a hydraulic passage connecting the pressure adjusting valve to the solenoid valve for supplying the output hydraulic pressure of the hydraulic pressure source to the hydraulic passage after reducing it by a first proportional solenoid valve, and a second proportional solenoid valve disposed between the hydraulic pressure supply passage and a reservoir to reduce the hydraulic pressure supplied from the hydraulic pressure supply passage, thereby carrying out automatic brake control.
In the vehicle hydraulic brake device as disclosed in JP patent publication 11-139279, if brake operation is performed by the driver during automatic brake control, it is necessary to detect the brake operating amount by means of a hydraulic pressure sensor for detecting the output hydraulic pressure of the master cylinder to change over from automatic brake control to normal braking. But it is difficult to change over to normal braking the moment the control hydraulic pressure by automatic brake control (hydraulic pressure of the wheel cylinders) becomes equal to the output hydraulic pressure of the master cylinder. There is some time lag in the changeover timing. As a result, deceleration may suddenly increase or decrease during such changeover, producing uncomfortable feeling during driving.
Also, if the hydraulic pressure sensor fails, even if the brake is operated, braking force will not increase because the output hydraulic pressure supply passage from the master cylinder will not open, so that braking force will be insufficient.
An object of this invention is to reduce any change in deceleration during changeover from automatic brake control to normal braking and to maintain high safety even if the hydraulic pressure sensor fails.